Oh yeah I need to look at HBMNTM again don’t I. XD
GT6 Dynamite is probably a bit different. 1 Dust of it is 1/9th of a Block of Dust.
Using 1 Dust of it is enough to make a single Dynamite Stick that can blast away a 3x3x3 of normally resistant Blocks, if you want to blast harder stuff like Obsidian you need to put 2 Dust into a Stick of Dynamite.
In order for Dynamite Mining to actually make sense it also applies Fortune 5 to the harvested Ores, so people actually have an incentive to set up proper Dynamite production with all it’s different steps.
There is also a cheaper Gunpowder based Boomstick that does only Fortune 3.
My Dynamite is by the way a great way to harvest those dense clusters near Bedrock which require Explosions to be mined. 
Also worth noting is that GT6 Ores themselves do the thing later Vanilla MC has introduced with dropping a quantity of “raw Ore” when fortune harvested, so it makes still sense to do it even without those dense Bedrock Clusters.